There are a number of other organizations (academic and industrial) involved in the OTEC field:

http://otecnews.org https://www.globalotec.co/what-is-otec

However OceanBit seems to be the pioneer in attempting to design a system that optimized for Bitcoin mining solely (with the long-term hope that the R&D and operations for doing it for Bitcoin mining eventually helps OTEC become more feasible for providing baseload energy onshore.)

This might be how five years ago, only a small number of people (e.g., Steve Barbour) were gaining initial expertise in using waste gas from oil and gas operators as an energy source, and now Exxon and others are involved.